Method of segregating light metal floating on fused electrolyte and means therefor



Feb. 16, 1932. T. GRISWOLD, JR

HSTHOD OF SEGREGATING LIGHT METAL FLOATING ON .FUSED ELECTROLYIE AND MEANS THEREFOR Filed Oct. 26, 1929 3 Sheets-Sheet 1 w U /M /M l /w S \Q Z:///

INVENTOR T. GRISWOLDJR METHOD OF SEGREGATING LIGHT METAL FLOATING on Feb; 16, 1932.

FUSED ELECTROLYTE AND MEANS THEREFOR Filed Oct. 26, 1929 :s Sheets-Sheet 2 /./A .7/ Z N U Q i K Jaw W A.

INVENTOR Feb; 16, 1932.

T. GRISWOLD, JR METHOD OF SEGREGATING LIGHT METAL FLOATING ON FUSED ELECTROLYTE AND MEANS THEREFOR Filed Oct. 26, 1929 3 Sheets-Sheet 3 INVENTQR Patented Feh. 16, 1932 STATES PATENT OFFICE.

THOMAS GRISWOLD, JR., OF MIDLAND,-HICHIGAK, ASSIGNOR TO THE DOW GHEMICAL COHPANY, F MIDLAND, MICHIGAN, A CORIPOBATION OF HICHIGAN concerned with a novel method and means for arnrnon or snonneerme LIGHT METAL rrioa'rmo 01v ruse]; ELEcrnoLYrE AND MEANS rnnnnron Application filed October 26, 1929. Serial No. 402,593.

My invention relates to methods of collecting or segregating light metal formed by electrolysis of a fused bath, such metal being lighter than the bath and floating thereon. It relates specifically to such collection of magnesium metal liberated by electrolysis of a fused bath containing magnesium chloride.

Such metals as magnesium and others of the alkali and alkaline earth groups tend to oxidize or burn upon exposure to the air and/or to combine with other reactable gases and it has been customary to rotect the liberated metal floating on the ath from. contact with air and other reactable substances. It has further been found advantageous to collect the liberated metal upon a limited and selected area of the bath in order to facilitate both the coalescence of the individual floating globules into a consistent mass of molten metal prior to removal from the bath and in order further to eliminate from said co1- lected and so removed metal as much of the bath as conveniently possible. It has been found, further to be advantageous to so collect the metal to a considerable depth in a restricted area walled in to form what is generally called a collecting well, permitting the so segregated and collected metal to acquire a considerable depth still floating on the bath before removal from the bath. By such procedure the removal of the metal from the' bath may be intermittent and at considerable intervals, thereby restricting the uncovering and handling of the metal to definite separated intervals and also permitting the metal to more thoroughly separate from the bath and from impurities accompanying the globules of liberted metal, such bath and impuritiessettling out in the collecting zone into the bath below, upon which the collected metal floats.

Various methods andmeans have been proosed for so collecting, coalescing and puriing the liberated metal globules in such a collectingwell and the present invention is so doing.

To the accomplishment of the foregoing and related ends, the invention, then, consists of the steps and means hereinafter fully described and particularly pointed out in the claims, the annexed drawings and the following description setting forth in detail certain means and one mode of carrying out the invention, such disclosed means and mode illustrating, however, but one of various waysin which the principle of the invention may be used.

In said annexed drawings Fig. 1 is a general longitudinal cross sectlon of an electrolytic cell adapted to the electroylsis of a fused bath for the liberation therefrom of a metal which will float thereon, the section being taken upon the line AB of the'plan thereof shown in Fig. 3. Fi 2 is a general cross section of the cell 1 ustrated in Figs. 1 and 3.

The type and details of construction, size and other features in general of theelectrolytic cell are immaterial to the application of my invention, which maybe applied to any such cell provided means equivalent to those to be later described as comprised in the cell herein illustrated are provided for initially separating the cathode-and anode products and for leading by a natural flow or circulation,.or by induced circulation, the so initially separated globules of metal to a definite location, at which location the invention herein described may be appli d, 1mm

scribe the invention, however, as applied to the production of magnesium metal by the electrolysis of a fused bath containin magnesium chloride in an electrolytic cel such as illustrated in the drawings, such cell representing one type thereof which is suitable for the purpose and embodying the above mentioned features of design, permitting the ap licationof myinvention. y eferringnow to the drawings in the figures'of which similar reference characters are used to'indicate identical parts shown in the various views, 1 is the cell pot, shown as having a rectangular form in the plan, and containing two parallel compartments, 2 and 2, separated -in' part by an intermediate partition 3 integral with, or electrically consolidated with, the walls of the pot. Cast steel is an admirable selection of material for such a pot which-may have one-or more risers shown at 4 for connectin a current lead in such manner as to make t e A plurality of anodes 5 w ch may be of carbon are suspended from above in two parallel lines, dipping in the bath, the level'of which is clearly indicated in Figs. 1 and 2 on the line 66. In order to separate the cathode metal product from the chlorine gas anode product, any suitable construction may be employed, the one here illustrated comprising an inverted trough-like device 7 which may be apart of the ot or attached thereto located in the bath a ove the active cathode surfaces 8 of the pot, which device, it will be seen, is adapted to entrap and retain temporarily, as hereinafter ointed out the metal globules rising throng the bath from said principal cathode surfaces 8. There is further provided a plurality of tubular refractory curtain members 9 surrounding the individual anodes, said curtain members diparea of the 'pot and the anodes, as indicated ping in the bath and covering those portions of the inverted .trou h-like trap device 7, facing the anodes. Suc curtains are here shown supported u on the superstructure 10 of the cell upon a edge thereof. Such superstructure may be constructed of refractory material, such as. fire brick. Covers 11 are fitted about the anodes and rest upon the superstructure 10 and from above the bath, with said superstructure, gas com artments 12 for collectin the anode gas rising through the bath, an maintaining it separately from the metal entrapped below the surface of the bath. Such gas maybe led awa in any convenient manner. Openings 13 1n the covers are here shown in the plan whichmay be connected with a suitable duct for leading away the evolved and collected gas.

A collecting well 14 for the metal is here shown at one end of the cathode pot, being bounded by the pot wall and a partition 15 which form -arectangular. well rising above the surface of the'bath and extending well below such surface. f v

On either side of the metal codlecting well 14 are two dredging wells 16 shown in the plan "with covers applied. These wells serve for the introduction of a suitable dipper or other implement for the purpose of dredging accumulated sludge from the bottom ofthe pot. The metal collecting well is further fitted with a cover 17' to restrict access of atmospheric air to the surface of the metal collected therein. Such metal is indicated in the well and in the collecting traps by the cross-hatched areas. v

It be. understood that the collecting traps 7 entirely encircle'the metal liberating in dashed lines in the plan.

Communication between the metal 001.

. lecting trap 7 and the metal collecting well 14 pgt the cathode.v

' that portion of the deck 19 of the tra 7 which projects out into the collecting we In order now to transfer the metal collected-in the trap 7 to the collecting well 14, it is only necessary to provide a supply of a suitably inert gas in the metal trap 7 which will act through the tubular riser 18 as a gas lift in manner similar to the customary air liftused in raising water or other liquids. Such gas may be evolved together with the' metal under certain conditions, as, for instance, when a magnesium chloride feed is employed containing hydrogen from which hydrogen gas will be liberated and may col lect in whole or in part along with the metal in the traps, or an inert gas may be supplied from without under pressure suflicient to overcome the static head at the point of its introduction, said introduction being at any point convenient or desirable in the metal trapped area. For the purpose of illustrating the. application of the invention, I here show in Figs. 1 and 3 the introduction of the gas through a pipe 20 at a point adjacent to the tubular riser 18. Such gas maybe c0n-, veniently supplied by a small gas pump 21 which may draw gas through a pipe connection 22 from any available source or through pipe connection 23 from the space in the well above the metal, by means of which latter variation, the gas may be reused for the gas lifting eflect.

Such removal of the metal from the trap into the well will' cause the natural flow thereof in the trap towards and to the tubuar riser or gas lift along the deck of the metal collecting trap as indicated by the dashed arrows shown in Fig. 3. If the gas be-introduced intentionally from without, or by generation withinlthe bath at a point or points distant or removed from the gas lift, such gas entrapped along with the metal in the collecting traps will assist in forwarding the metal along the deck of the trap towards and to the gas lift. I

By means of the method and means hereinbefore disclosed I find it possible to collect the entrapped metal in the metal collecting well to a very considerable depth and to therein thoroughly segregate, coalesce or gravity through the so collected metal into the bath below. The metal may then be re moved in any preferred manner, as by dip ping, pumping, or otherwise, at widel or conveniently separated intervals, being eld safe and secure from oxidation or deterioration in the intervenin intervals in the collecting well, since during such intervals the inert gas used in the gas lift will blanket the surface of the metal beneath the cover of the .Well and effectively protect it from attack.

A number of gases may be used, such as hydrogen, S0 CO or the products of combustion of carbonaceous fuel. Hydrogen is, in practice, sometimes formed along with the metal due to the inclusion of some water with the feed and such part of the hydrogen as may be entrapped along with the metal serves to operate the gas lift feature. Additional gas may be supplied as indicated through pipe 22 if insuflicient hydrogen is.

liberated in the bath to effectively operate the gas lift feature.

It will be seen that the invention accomplishes the purpose intended in an extremely simple and effective manner without the use' of any moving mechanical part in the. bath, in which, owing to the high temperature, such moving part is undesirable. The gas pump may be obtained in a variety of forms,

maybe located at any convenient point, and may serve any number of individual cell units. It will be further seen that the invention may be applied as hereinbefore indicated to the collection of a light metal produced in any electrolytic cell and floatable upon the fused bath, provided such metal is, as required in all such apparatus, effectively initially separated upon liberation from theanode product, it being merely necessary to apply the gas lift feature to the so initially collected metal and provide a suitable well for receiving the so lifted metal. The invention further constitutes a valuable improvement in the art, accomplishing in a very simple manner what has heretofore been either impossible or only accomplished by hand or by means of mechanical devlces operating in the bath under conditions of.

high temperature and generally requiring journal bearings which are disadvantageously applicable under the conditions existing.

Other modes of applying the principle of my invention may be employed instead of theone explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out and dis tingtly claim as my invention '1. In a method of the character described, the step which consists in employing a gas for the purpose of directly lifting ,molten metal above the surface level of the bath.

2. In a method of the character described, the step which consists in em loying a mixture of gas and molten metal fbr the purpose of lifting said metal above the surface level of the bath.

3. In a method of the character described, the step which'consists in admitting gas to admixture with molten metal in a suitable duct below the surface of the bath for the purpose of lifting said metal above the surface level of said bath into a receiving well without change of state.

4. In a method of the character described,

the step which consists in leading a mixture 4 of gas and molten metal, buoyant with respect to the bath from which the metal has been liberated, to a level above the surface level of said bath into a receiving well without change of state.

6. In a method of the character described, the steps'which consist in leading a mixture of gas and molten metal, buoyant with respect to the bath from which the metal has been liberated, to a level above the surface level of said bath, and separating said mixture.

7. In a method of the character described, the steps which consist in leading a mixture of gas and fluid metal, buoyant with respect to the bath from which the metal has been liberated, to a level above the surface level a duct connecting between said trap and said well adapted to act as a gas lift for the metal.

9. In apparatus of the character described, the-combination of a trap submerged in the bath adapted to initially collect metal which has been liberated in said bath, a collecting well for metal separated from the bath by walls extending both above and below the surface level of the bath, said well communicating with the bath at its lower level, a duct connecting between said trap and said well adapted to act as a gas lift for the metal, and means to supply a current of gas to said duct.

10. In apparatus of the character described,

the combination of means for initially collecting light metal cathode product separately from anode product, a partitioned zone in said bath, and a duct leading from the means for initially. collecting metal to said zone adapted to lead a mixture of metal and gas to said zone.

Signed by me, this 22 day of October, 1929.

THOMAS GRISVVOLD, J R. 

